Olive trees by-products (OTB) has high fiber and low protein content that could limit its use for feeding animals. This work aimed to investigate the effect of replacement of berseem hay in the diet of lactating Barki ewes by OTB treated with increasing levels of urea on Animal's nutrient digestibility, milk yield and milk composition. Thirty-five of lactating Barki ewes after one week of parturition were randomly assigned to five groups (seven each). The first; control group (CBH) was fed concentrate feed mixture (CFM) plus berseem hay. The second group (UOTB) was fed CFM + untreated OTB as a replacement of berseem hay.  While, OTB2, OTB4 and OTB6 groups were fed CFM + OTB treated with 2%, 4% and 6% urea (on DM), respectively. Urea treatment significantly improved the crude protein (CP) while decrease fiber fractions content of the treated OTB. Total volatile fatty acids (TVFA's), total protein, NPN and ammonia N levels in the rumen were increased (p<0.05) in all groups fed OTB treated with urea. Daily milk yield, fat corrected milk (FCM) and composition were slightly increased in groups fed treated OTB compared to both untreated OTB and control group. Ewes fed OTB treated with 4% urea had the highest values (p<0.05) for milk production and it's composition. Feeding olive trees by-products treated with 4% urea as a replacement of berseem hay significantly improved nutrients digestibility and milk production performance of Barki ewes.